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An early study demonstrated that washing embryos was effective for removal of virus after artificial exposure of in vivo-derived embryos to a cytopathic isolate of BVDV (Singh et al., 1982 Theriogenology 17,437–444). However, a recent study using representative noncytopathic isolates of BVDV demonstrated that washing was less beneficial for removing some isolates of BVDV than for others (Waldrop et al., 2000 Theriogenology 57, 575). Thus, the objective of this study was to determine if the quantity of a high affinity isolate of BVDV that remains associated with single-washed or trypsin-treated embryos is sufficient to cause infection in vivo. Twenty zona pellucida-intact Day 7 morulae and blastocysts (MB) were collected from superovulated cows. After collection, all MB were washed according to International Embryo Transfer Society (IETS) standards, and all but 4 (negative controls) were exposed for 2 h to approximately 106 cell culture infective doses (50% endpoint) per mL (CCID50/mL) of viral strain SD-1. Following exposure, one-half of the MB were washed and one-half were trypsin-treated according to IETS standards. All MB were then individually sonicated, and sonicate fluids were injected intravenously into seronegative calves. Blood was collected from each calf on Days 0, 3, 6, 9, 12, 15, 20, 25, and 30, and sera were assayed for BVDV and anti-BVDV antibodies. All cattle used in the study were determined to be virus- and antibody-negative 30 d prior to and the day of intravenous inoculation of sonicate fluids into calves. Viremia was not detected in any calf following injection, possibly due to intermittent sampling and/or small amount of embryo-associated virus present. However, seroconversion of 38 and 13% of the calves occurred following injection with sonicate fluids from washed and trypsin-treated embryos, respectively. Findings demonstrated that the quantity of a high affinity isolate of BVDV associated with single-washed or trypsin-treated embryos is sufficient to be infective in vivo as evidenced by seroconversion. These results emphasize the need for studies to determine if the virus associated with exposed individual embryos constitutes an infective dose when placed into the uterus.

186SEROCONVERSION OF CALVES TO BOVINE VIRAL DIARRHEA VIRUS (BVDV) FOLLOWING INTRAVENOUS INOCULATION WITH ARTIFICIALLY EXPOSED IN VIVO-DERIVED EMBRYOS